Selective Analysis of Sulfur-Containing Species in a Heavy Crude Oil by Deuterium Labeling Reactions and Ultrahigh Resolution Mass Spectrometry.

Xuxiao Wang,Wolfgang Schrader

doi:10.3390/ijms161226205

Abstract

A heavy crude oil has been treated with deuterated alkylating reagents (CD3I and C2D5I) and directly analyzed without any prior fractionation and chromatographic separation by high-field Orbitrap Fourier Transform Mass Spectrometry (FTMS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) using electrospray ionization (ESI). The reaction of a polycyclic aromatic sulfur heterocycles (PASHs) dibenzothiophene (DBT), in the presence of silver tetrafluoroborate (AgBF4) with ethyl iodide (C2H5I) in anhydrous dichloroethane (DCE) was optimized as a sample reaction to study heavy crude oil mixtures, and the reaction yield was monitored and determined by proton nuclear magnetic resonance spectroscopy (1H-NMR). The obtained conditions were then applied to a mixture of standard aromatic CH-, N-, O- and S-containing compounds and then a heavy crude oil, and only sulfur-containing compounds were selectively alkylated. The deuterium labeled alkylating reagents, iodomethane-d3 (CD3I) and iodoethane-d5 (C2D5I), were employed to the alkylation of heavy crude oil to selectively differentiate the tagged sulfur species from the original crude oil.

Highlights

The demand for affordable and reliable energy leads to a continuous focus on fossil-based materials, and nowadays the trend is shifting to heavier petroleum resources
Ultrahigh-resolution MS has an unparalleled advantage for crude oil analysis, but as of yet, not all compositions present in heavier petroleum can be completely and accurately analyzed by any single available analytical method
It has been shown that Ag+ ions kinetically coordinate preferentially to sulfur atoms instead of oxygen or nitrogen atoms to form metal-ligand bonds [20,25]

Summary

Introduction

The demand for affordable and reliable energy leads to a continuous focus on fossil-based materials, and nowadays the trend is shifting to heavier petroleum resources. One of the huge disadvantage of heavy crude oils as energy supply is that they contain rich heteroatoms, such as sulfur, nitrogen and oxygen. A better understanding of heavy crude oil composition is necessary for that aim. Heavy petroleum is a supercomplex [1] mixture of hydrocarbons containing various amounts of heteroatoms (N, O and S), and it challenges and promotes the development of analytical techniques [2]. Mass spectrometry has been established as the most powerful and promising method to characterize such complex mixtures [3,4]. FT-ICR MS provides sufficient mass resolving power and mass accuracy to identify each of the thousands of different molecules and their elemental compositions from the most complex mixtures [5]. A new commercially available type of the high-field Orbitrap FTMS, the Orbitrap Elite [6,7,8], has been evaluated and employed successfully to analyze the petroleum samples with a resolving power of up to 900,000 at m/z 400 [9,10]

Methods

Results

Conclusion